Directed self assembly (DSA) of block copolymers is a method useful for generating patterned features for the manufacture of microelectronic devices, wherein the features have critical dimensions (CD) on the order of 2-50 nm (nanometers). Templated DSA methods have been used to extend the resolution capabilities beyond what may be obtained with conventional lithography. In a conventional lithography approach, ultraviolet (UV) or other radiation may be used to expose an image, using a transmission or reflecting mask, onto a photoresist layer coated on a substrate. This approach is limited by such factors as the physics of diffraction and shot noise. On the other hand, DSA techniques, such as graphoepitaxy and chemoepitaxy, may enhance resolution while reducing CD variation, when used in conjunction with conventional lithography.
Block copolymers used in DSA may comprise a removable polymer block having a given repeat unit and one or more additional blocks that may remain after the first block is removed, each, respectively, having another repeat unit. In any case, the block copolymer is coated, on a substrate, and allowed to phase separate or align during annealing. The annealed polymer exhibits an inherent pitch or repeat distance, while the individual separated blocks each exhibit an inherent width, usually determined by their respective molar masses. While it is possible to ascertain the inherent pitch of the block copolymer and inherent widths of the individual blocks after an undirected annealing step, a more accurate and precise measurement is usually accomplished after directed self assembly.
As noted supra, DSA may be accomplished by graphoepitaxy or chemoepitaxy, inter alfa. In graphoepitaxy, a block copolymer self organizes according to a substrate that may be patterned with conventional lithography (UV, Deep UV, e-beam, EUV, or ion beam, for example) to form repeating topographical features such as lines and spaces (LS), extended or segmented trenches, extended or segmented rails, contact holes (CH) or other patterns useful in semiconductor manufacture. In one example of a LS directed self assembly array, a selected block copolymer, having approximately an integer number of inherent pitch distances of the block copolymer relative to the pitch distance between printed lithographic rails can form a self-aligned pattern between the rails that is an integeral multiple of the rail-to-rail distance. Such an integral relationship may be termed commensurate or multiply commensurate. In addition, posts and linear and shaped segmented rails may be used to direct the self assembly of a block copolymer into more complex lithographic patterns. For example, Yang et al. in U.S. Pat. No. 8,309,278 disclose a template for this purpose comprising a two-dimensional array of first posts, wherein the first posts are spaced apart from each other in a first direction by a first spacing Lx and in a second direction by a second spacing Ly, and a second post disposed near one of the first posts, wherein the second post is spaced apart from the one of the first posts by a third spacing, wherein the third spacing is different than the first spacing Lx and the second spacing Ly; and a polymer pattern self-assembled on the template, wherein the first spacing Lx and/or the second spacing Ly is commensurate with an equilibrium periodicity La, commonly also known as Lo, of a block copolymer of the polymer pattern, and wherein the second post is disposed at a position of a bend in the polymer pattern.
In chemoepitaxy, a block copolymer self organizes according to a substrate that may be patterned (using UV, Deep UV, e-beam, EUV, or ion beam lithography, for example) to form repeating patterns of differing chemical affinity. These have little or no topographical patterning but can align the separated phases of the block copolymer by “pinning” one of the blocks to the region on the substrate to which that block has affinity. In one example of a line space directed self assembly array, a selected block copolymer, having approximately an integer number of inherent pitch distances relative to the distance between patterned affinity areas, can form a self-aligned pattern between those areas that is an integral multiple of the rail-to-rail distance. Such a condition may be termed commensurate or multiply commensurate. Affinity regions may comprise a neutral region, having similar affinity for either of the blocks, punctuated by regions having an affinity for one of the polymer blocks. The affinity may be introduced to the surface using plasma etch processes, exposure to light or other radiation such as electron beams or ion beams, patterning with a standard lithographic material such as a photoresist, and depositing a thin layer on the surface using chemical vapor deposition, evaporation, sputtering or other deposition process or image-wise treating with a coupling agent such as a silylation agent. For example, in U.S. Pat. No. 8,226,838, Cheng et al. disclose a method of forming polymer structures comprising: applying a solution of a diblock copolymer assembly comprising at least one diblock copolymer that forms lamellae, to a neutral surface of a substrate having a chemical pattern thereon, the chemical pattern comprising alternating pinning and neutral regions that are chemically distinct and have a first spatial frequency given by the number of paired sets of pinning and neutral regions along a given direction on the substrate; and forming domains comprising blocks of the diblock copolymer, wherein the domains formed by lateral segregation of the blocks, wherein at least one domain has an affinity for the pinning regions and forms on the pinning region, and wherein the domains so formed are aligned with the underlying chemical pattern, wherein domains that do not form on the pinning region form adjacent to and are aligned with the domains formed on the pinning regions, such that a structure comprising repeating sets of domains is formed on the chemical pattern with a second spatial frequency given by the number of repeating sets of domains in the given direction, the second spatial frequency being at least twice that of the first spatial frequency.
Neutral layers are layers deposited on a substrate or the surface of a treated substrate which have little or no preferential affinity for either of the block segments of a block copolymer employed in directed self assembly. In graphoepitaxy, neutral layers within or surrounding lithographic features may allow the proper placement or orientation of block polymer segments which leads to the desired pattern. In chemoepitaxy, modification of selected areas of the neutral layer occurs so that they have affinity for one of the blocks of the block copolymer; thus pinning that block to the modified portion and resulting in the desired pattern and allowing the copolymer blocks to self-assemble on the neutral portion.
Both graphoepitaxy and chemoepitaxy have been demonstrated. However, each of these two methods has limited use in generating patterns with high resolution and low CD variation, for different reasons. For example, in graphoepitaxy, the placement accuracy and edge roughness of the block-copolymer domains deteriorates during pattern formation due to variation in thickness uniformity of the over-coating of polymer film and due to imperfections in the topographical pre-patterns. The graphoepitaxy process also typically results in formation of a half-width domain next to each of the sidewalls so that the pattern spacing across the subdivided channel is not uniform. While chemical epitaxy may allow a gain in CD control because of its lower topography, the options for image wise chemical modification of surfaces are limited, which may result in inadequate pinning of one of the blocks of the block copolymer.
Thus, due to the aforesaid limitations, there remains a need for a directed self assembly method that employs a template that is capable of providing strong image-wise pinning of one or more blocks of the block copolymer.